Volume 5 Supplement 1
Uv induced ds(ss)-DNA damage: optical and electrical recognition
© The Author(s) 2005
Published: 31 May 2005
The main targets for UV irradiation in biological cells are DNA molecules . Photochemical reactions in DNA caused by UV irradiation are the general processes that we use, in cell biology, to study the DNA damaged area. We analyzed:
known mechanisms of UV induced DNA damage in cells: excited by UV light, nucleotide bases begin to take part in photochemical reactions of cyclobutane-pyrimidine dimmer and (4–6) adducts formation.
absorption DNA spectrum behaviour in the range 200 – 300 nm changes of absorption by bases under UV irradiation.
photoluminescence charge transport behaviour of ds-DNA molecules in wet, dry adsorbed layers with bases changes under UV irradiation.
Then the experimental investigations were carried out on 2 mM plant ds-DNA polymerized molecules (Eris, France ) that were dissolved in 3 mM NaOH buffer and 2 mM ss-DNA with 15 oligonucleotides bases: 3'-CCA CCG CTG CTG AGG-5', length 5,4 nm, wide 1 nm (Jena BioScience, Germany) were dissolved in 100 mM carbonate/bicarbonate buffer . We prepared ds-DNA polymerized molecules water solutions dissolving 0,1 ml of DNA in buffer solution in 1, 40, 50 ml of water showed a pH of 7,4 (the volume ratios are 1:1, 1:40, 1:50, correspondingly) and ss-DNA water solution dissolving 1 ml of DNA in buffer solution in 5 ml of water showed pH of 7,4. The solutions in quartz cuvettes were irradiated by UV (Л = 200–400 nm) during 5–90 min with the light power 1020 photon/(cm2 s).
From absorption spectra of different concentration of ds(ss)-DNA molecules in water solution the influence of UV irradiation on ds(ss)-DNA molecule absorption were revealed.
Photoluminescence spectra of wet dsDNA layer with networks have maxima at 432, 440 and 454, 463 nm before and after UV irradiation with 337 nm and 365 nm during one hour, respectively. The presence of photochemical reactions appear in the decreasing of photoluminescence intensity in this layer. Then it is possible intensive emission with participation of electronic states corresponds to molecular orbital systems in the nucleotide base pairs and sides of the ladder having a periodic structure with alternating sugar and phosphate groups. A part of the electron levels that determine photoluminescence spectrum can correspond the formation of dsDNA molecular networks.
The presence of the photochemical reactions appear in the decreasing of dry absorbed ds-DNA molecular layer with networks conductivity under periodical switched UV irradiation: as a result the conductivity decreases after first radiation reflecting the reducing of pyrimidine bases (that formed dimmers) contributing to ds-DNA conductivity. The increase of the conductivity value after UV irradiation could be caused by the particular reparation of ds-DNA under applied voltage of 1 V.
UV induced ds(ss)-DNA damage in buffer solution and in wet, dry absorbed layer, using optical and photoluminescence spectroscopy, as well as conductivity was revealed. Models of UV induced ds(ss)-DNA damage were accounted in the photochemical reactions of cyclobutane-pyrimidine dimmer and (4–6) adduct formation were used to recognise ds(ss)-DNA damage in their absorption spectra and wet ds-DNA damage in photoluminescence spectra and in the behaviour of conductivity under periodical switched of UV irradiation.
But it's important to develop offered methods for its further ability to direct evident possible photochemical reaction that took place in ds (ss)-DNA.
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